`testOpLazyConnectedComponents.TestOpLazyCC.testParallel` fails sometimes

[k-dominik]

It fails quite reproducibly on CircleCI and occasionally also on my machine.

Sample output:

======================================================================
FAIL: testParallel (testOpLazyConnectedComponents.TestOpLazyCC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ubuntu/lazyflow/tests/testOpLazyConnectedComponents.py", line 375, in testParallel
    assert_array_equal(out[i].squeeze(), out[i+1].squeeze())
  File "/home/ubuntu/miniconda/envs/test-env/lib/python3.6/site-packages/numpy/testing/utils.py", line 871, in assert_array_equal
    verbose=verbose, header='Arrays are not equal')
  File "/home/ubuntu/miniconda/envs/test-env/lib/python3.6/site-packages/numpy/testing/utils.py", line 796, in assert_array_compare
    raise AssertionError(msg)
AssertionError: 
Arrays are not equal

(mismatch 100.0%)
 x: array([[1, 1, 1, ..., 1, 1, 1],
       [1, 1, 1, ..., 1, 1, 1],
       [1, 1, 1, ..., 1, 1, 1],...
 y: array([[2, 2, 2, ..., 2, 2, 2],
       [2, 2, 2, ..., 2, 2, 2],
       [2, 2, 2, ..., 2, 2, 2],...
-------------------- >> begin captured stdout << ---------------------
{1, 2}